As a solid dosage form, the tablet is the most popular and useful form of oral medication for dispensing active ingredients such as pharmaceuticals, vitamins, and minerals. The compressed tablet offers several advantages over other solid dosage forms. These advantages include greater accuracy of dosage, more convenient administration, increased durability and stability during storage, shorter production time, and economy and efficiency in storage, packaging and shipping.
Tablets can be prepared using several established methods such as wet granulation, dry granulation, and direct compression. The most desirable method from the standpoint of the processing procedures, equipment and materials is the direct compression method. This method increases the efficiency of tableting operations and reduces costs by requiring the least amount of space and labor.
In a dry direct compression method, the ingredients are simply dry-mixed and then compressed. There is no granulation stage. It is essential that each component is uniformly dispersed within the mixture. Any tendency for component segregation must be minimized to assure that each tablet contains an accurate reproducible dosage. In addition, the mixture must have certain flow characteristics to allow accurate and convenient transport and must be cohesive when compressed. To reduce segregation tendencies the particle size distribution, shape, and density of all the ingredients should be similar. There are only a few substances available in forms which could be compressed directly without further treatment. If these ingredient characteristics are not present, then one of the granulation methods should probably be used.
There are some limitations to the use of direct compression tableting. First, while compression of some components may produce tablets that do not disintegrate, other components of the tablet may interfere with the compressibility of the tablet composition and thus minimize the usefulness of this method. Second, most materials possess relatively weak intermolecular attraction thereby affecting the compacting of the ingredients into tablets. Third, with some formulations, the percentage of active ingredient is so small that direct compression would be impractical and uneconomical. However, in this case, an inert compressible diluent can be used to increase bulk in order to make the tablet a practical size for compression.
The direct compression method is a rather simple procedure compared to the more complicated and time consuming wet process method. Relatively inexpensive and unreactive chemicals are commonly used as the major component in direct compressible formulations. However, only a very limited number of materials possess the necessary cohesive strength and flowability to allow direct compression without requiring granulation. Modification is often required either by treating the material in some manner during the earlier stages of preparation or by adding a binder or excipient material which will surround or coat the active ingredient thereby forming an easily compressible excipient. The limitations associated with the direct compression method are of particular concern when tableting an active ingredient such as carbonyl iron. Therefore, a composition and method for tableting carbonyl iron by the direct compression technique is an important development in the art.